A laminate sheet material suitable for use as imitation leather products in the production of shoes, handbags and the like has been prepared by casting a thin film of a flexible urethane resin polymer onto the surface of a napped and sheared fabric sheet. There are several problems associated with the production and the use of such imitation leather products. First, the fabric which is napped and sheared several times to raise the surface presents a nonuniform surface due to such surface treatment, and, further, is quite expensive and its supply limited. The wear resistance and aesthetic appearance of the imitation leather product containing a thin urethane film often are not satisfactory, since the raised napped and sheared fabric contains surface whiskers which often tend to protrude through the thin resin film, either during production, or particularly when the imitation leather material is placed under pressure in use, such as when used as a shoe upper material.
Various attempts have been made to replace the fabric base with other materials, such as a layer of foam material. Polyvinyl chloride and urethane foams are generally not acceptable for use in shoe upper laminates. The use of latex formulations to form a thin foam layer to date has been unsuccessful, since the latex polymers have often suffered from various degrees of low wall-cell strength, and from mud cracking in the surface during the drying of the wet foam latex layer. Such foamable latex formulations are often prepared employing natural or synthetic elastomeric polymers, together with thickeners, foaming agents, catalysts, fillers, surfactants, curing agents and the like.
One class of foamable latex formulations includes the employing of carboxylated elastomers, such as diene-conjugated elastomers like butadiene-acrylonitrile copolymers. Such formulations also include water-soluble curing agents to effect cross-linking of the wet foam structure on heating, such as by the use of various water-soluble amino resins like melamine-formaldehyde condensates, or other curing compounds. Such cross-linkable latex formulations are set forth, for example, in U.S. Pat. Nos. 2,871,213 and 3,215,647. In order to provide for the preparation of wet foams or the use of the latices, these latex formulations typically include small amounts of silicone-type surfactants to promote small and uniform cell development.
In addition, such latex formulations almost invariably include long-chain fatty acid soaps, particularly ammonium stearate, as a foaming agent, and, in addition, various thickeners are often employed, typically in amounts of less than 1% by weight, in order to adjust and provide the latex formulation with suitable foaming viscosity. Such thickeners include ethyl cellulose, carboxymethyl cellulose, polyvinyl pyrrolidone and various polymers, which are added in small amounts. The latex formulations also often contain various amounts of fillers to reduce the cost and to aid in providing the desired viscosity. These latex formulations are alkaline, and are prepared in foam form by whipping air into the formulation through a mechanical mixing, such as through the technique of employing an Oakes foamer. The typical foamable latex formulations and the uses for which they are employed, such as foam-backed drapery fabrics, are set forth, for example, in U.S. Pat. Nos. 3,231,533; 3,491,033; 3,527,654; 3,598,770; and 3,607,341 and others.